The invention relates to a method of manufacturing iron garnet layers having refractive indices n adjusted in a defined manner and lattice constants a.sub.o adjusted in a defined manner, in which the layers are deposited on a substrate by means of rf cathode sputtering using a target consisting substantially of an iron garnet phase besides residual phases of substantially the same sputtering rate in a noble gas plasma of an ion energy of the ions bombarding the growing layer of smaller than 10.sup.2 eV and a pressure in the range from 0.1 to 2.0 Pa.
Such a method is known from German Patent Application P 3704378.1. Layers which are manufactured according to they known method are used for the building-up of optical waveguides for non-reciprocal optical components. By means of the known method it is possible in particular to vary the refractive index n of the deposited layers by up to 0.7% by variation of the gas pressure of the plasma in the range from 0.3 to 0.8 Pa, in which the values for the refractive indices and for the lattice constants decrease with increasing gas pressure. It is assumed that the dependence of the refractive index n on the pressure of the plasma, for example, an argon plasma, is substantially the result of the variation of the bombardment of the growing layer by low energetic ions, in this case argon ions. As a result of the different back-sputtering rates of the elements taking part in the building-up of the layer, the composition of the manufactured layer varies and hence the value for the refractive index n and for the lattice constant a.sub.o also varies.
It has proved in practice that a larger variation width of the values for the refractive index n and the lattice constant a.sub.o of the deposited layers is desired, for example, to enable the optical adaptation of partial layers of a waveguide structure. This is of importance in particular when several targets are to be used for the manufacture of a waveguide structure.